DMA2D: adding transparency to a bitmap - is it possible? ((A)RGB + A8 blending)

[TDJ]

I have ARGB bitmap image and I would like to blur its edges by applying A8 mask.

Is it possible to do it with DMA2D Chrom-Art? I cannot figure it out.

Note: it is not the same as blending masked solid color with background, e.g. to draw anti-aliased font.

In another words, I want to replace (or mix) my bitmap alpha channel with A8 mask bits without changing RGB values.

[KDJEM.1]

Hello @TJast​,

Could you please provide more details, such as the MCU you are using.

For example with STM32F7, the DMA2D has four operating modes:

• Register-to-memory for rectangle filling operation,
• Memory-to memory for 2D memory copy operations,
• Memory to memory with pixel format conversion for bitmap drawing with format conversion,
• Memory to memory with pixel format conversion and blending for bitmap or text drawing with transparency.

For more explanation, I advise you take a look at this presentation.

Thank you.

Kaouthar

[TDJ]

@KDJEM.1​ Thank you for your answer. The exact MCU I am dealing with is STM32F769NI.

I am aware of the four supported CR modes and three AM (alpha modes). However, it seems to that none of the possible combinations allows to accomplish what I am looking for, that is, combining RGB bitmap with another bitmap containing alpha A8 bytes only WITHOUT blending (A+ARGB->ARGB), just replacing one alpha bitmap value for another.

[TDJ]

@KDJEM.1​ I know the answer- it is not possible as it would require two "foregrounds".